MEASURMENT AND ANALYSIS OF AGRICULTURAL PRODUCTIVITY IN COLOMBIA

Worldwide agricultural commodity prices boomed from 2006 to 2011, peaking u

Wealthy and Healthy in the South Pacific

Objectives- The main aim of this paper is to analyse the relationship between socio-economic status and health status at the household level in Fiji, a developing country in the South Pacific, based on original household survey data compiled by the authors Method- We exploit the geographic conditions of Viti Levu, the relatively small main island of Fiji, to isolate the effects of household wealth on health. For households on this island physical distance is not a significant impediment for access to health care and other publicly-provided services. We use a constructed index of household wealth in place of the more commonly used income measure of socio-economic status. To control for reverse causality and other possible sources of endogeneity we use an Instrumental Variable strategy in the regression analysis. Findings- We find that a household’s socio-economic status, as measured by a constructed wealth index, has a substantial impact on the household’s health status. We estimate that if a household's wealth increased from the minimum to the maximum level, this would decrease its probability of being afflicted by an incapacitating illness by almost 50 per cent. Conclusions- Health outcomes from existing health services can therefore be improved by raising the economic well-being of poor households. Conversely, the provision of additional health services alone may not necessarily improve health outcomes for the poorest.

Economics of U.S. government debt accumulation

The United States of America is an indebted nation in the early years of the new millennium, changing from $469 billion in 1973 to$14 trillion in 2010, as spending is justified on the basis that it promotes GDP growth which in turn increases societal benefits. Despite the benefits of debt, its effectiveness and the transmission mechanisms of fiscal policy are still on debate. Consequently, the economic effects of U.S. government debt accumulation are studied in three empirical research articles. The dissertation is composed of five chapters. The first chapter is an introduction wherein the problem statement, the purpose, objectives and justifications are discussed. Then, the three articles are presented. The analyses used dynamic econometric models and data in the post Bretton Woods system of monetary management. Finally, the results are summarized in the fifth chapter. The first article studied the effects of government debt on employment and the unemployment rate. The results indicate that debt has positive effects on employed labor in the economy in the long run, and it was found effective at retaining and decreasing the unemployment rate. Moreover, an unemployment rate shock produced a hump-shaped response of government debt. The second article studied the effects of government debt on exports. The causality tests did not provide evidence to support a relationship among those variables; however, the response of exports to a debt shock was positive and hump-shaped. Finally, the third article studied the transmission of U.S. government debt shocks into the Mexican economy; the results indicate that debt produces positive externalities as its GDP grows. Moreover, Mexican GDP is favored by increasing U.S. GDP; furthermore, a positive U.S. employment shock produced a hump-shaped response of Mexican GDP. In conclusion, U.S. government debt depreciates the currency which leads to price fluctuations of output and the inputs of production; in turn, the economy is likely to experience growth in exports, GDP, and employment that favors the economic growth of Mexico through trade. Finally, future research endeavors in the economics of government debt accumulation may contemplate to study the cooperative interdependence among political institutions involved in fiscal and economic policies

Socioeconomic Status and Health Outcomes in a Developing Country

While the relationship between socioeconomic status (SES) and health is well documented for developed countries, less evidence has been presented for developing countries. The aim of this paper is to analyse this relationship at the household level for Fiji, a developing country in the South Pacific, using original household survey data. To allow for the endogeneity of SES status in the household health production function we utilize a simultaneous equation approach where estimates are achieved by full information maximum likelihood. By restricting our sample to one, relatively small island, and including area and district hospital effects, physical geography effects are unpacked from income effects. We measure SES, as permanent income which is constructed using principal components analysis. An alternative specification considers transitory household income. We find that a 1% increase in wealth (our measure of permanent income) would lead to a 15% decrease in the probability of an incapacitating illness occurring intra-household. While presence of a strong causal relationship indicates that relatively small improvements in SES status can significantly improve health at the household level, it is argued that the design of appropriate policy would also require an understanding of the various mechanisms through which the relationship operates.

Holographic s+p Superconductors

We study the phase diagram of a holographic model realizing a U(2) global symmetry on the boundary and show that at low temperature a phase with both scalar s and vector p condensates exists. This is the s+p-wave phase where the global U(2) symmetry and also the spatial rotational symmetry are spontaneously broken. By studying the free energy we show that this phase is preferred when it exists. We also consider unbalanced configurations where a second chemical potential is turned on. They present a rich phase diagram characterized by the competition and coexistence of the s and p order parameters.Comment: 6 pages, 4 figures; v3: published version, clarifications and references adde

Statistical mechanics as guidance for particle-based computational methods

Particle-based methods apply some laws of Classical Mechanics to all the particles of a granular system. On the other hand, classical Statistical Mechanics deals with systems consisting of a lot of particles, focusing on the statistical distribution of some intensive properties. Consequently, the macroscopic behaviour and the average properties of the system in equilibrium are based on some microscopic considerations. To do that, statistical tools and mechanical laws are used together. For an implemented particle-based method to be realistic enough, then the obtained simulations should satisfy some basic underlying physical requirements, and Statistical Mechanics is a useful tool to establish such requirements. This paper presents some results based on Statistical Mechanics that are useful for a realistic modelling of granular systems using Particle-based methods. Examples of the discussed issues include that the same protocol makes a disordered granular medium attain always the same packing ratio; that some local arrangements are less probable than others; that there is a well-established limit to the achievable density of granular assemblies of hard spheres; and that the equilibrium of disordered granular systems does not coincide to the state of minimum potential energy (which would be get in a completely ordered arrangement). The consideration of such issues in practical applications could be helpful to save time in computational methods, to avoid mistakes or, at least, to verify that the implementations are realistic

Statistical mechanics approaches to granular media: between micromechanics and macromechanics

The mechanical behavior of granular materials has been traditionally approached through two theoretical and computational frameworks: macromechanics and micromechanics. Macromechanics focuses on continuum based models. In consequence it is assumed that the matter in the granular material is homogeneous and continuously distributed over its volume so that the smallest element cut from the body possesses the same physical properties as the body. In particular, it has some equivalent mechanical properties, represented by complex and non-linear constitutive relationships. Engineering problems are usually solved using computational methods such as FEM or FDM. On the other hand, micromechanics is the analysis of heterogeneous materials on the level of their individual constituents. In granular materials, if the properties of particles are known, a micromechanical approach can lead to a predictive response of the whole heterogeneous material. Two classes of numerical techniques can be differentiated: computational micromechanics, which consists on applying continuum mechanics on each of the phases of a representative volume element and then solving numerically the equations, and atomistic methods (DEM), which consist on applying rigid body dynamics together with interaction potentials to the particles. Statistical mechanics approaches arise between micro and macromechanics. It tries to state which the expected macroscopic properties of a granular system are, by starting from a micromechanical analysis of the features of the particles and the interactions. The main objective of this paper is to introduce this approach

Equations of state in soil compression based on statistical mechanics

The authors have published a very interesting contribution in which they present a new and general relationship between void ratio and overburden pressure in the compression process of soils. The study is based on the law of interparticle energy distribution used in statistical mechanics and, in particular, the compression process of a soil is described according to its initial and final void ratios, and to a parameter /? which is related to the potential energy of a soil element. Such potential energy depends not only on the mass and elevation of soil particles, but also on the interactions between them. To account for such interactions, the authors introduce the concept of "imaginary particles", which allows them to use empirically-calibrated P values in the formulation without the need to consider interparticle interactions explicitly. In fact, the results presented by the authors show that such approach reproduces successfully the compression behaviour of a wide range of situations and soils

Statistical distributions obtained from the compression of monodisperse, soft and frictionless particles

The cyclic compression of several granular systems has been simulated with a molecular dynamics code. All the samples consisted of bidimensional, soft, frictionless and equal-sized particles that were initially arranged according to a squared lattice and were compressed by randomly generated irregular walls. The compression protocols can be described by some control variables (volume or external force acting on the walls) and by some dimensionless factors, that relate stiffness, density, diameter, damping ratio and water surface tension to the external forces, displacements and periods. Each protocol, that is associated to a dynamic process, results in an arrangement with its own macroscopic features: volume (or packing ratio), coordination number, and stress; and the differences between packings can be highly significant. The statistical distribution of the force-moment state of the particles (i.e. the equivalent average stress multiplied by the volume) is analyzed. In spite of the lack of a theoretical framework based on statistical mechanics specific for these protocols, it is shown how the obtained distributions of mean and relative deviatoric force-moment are. Then it is discussed on the nature of these distributions and on their relation to specific protocols

Holographic Type II Goldstone bosons

The Goldstone theorem implies the appearance of an ungapped mode whenever a continuous global symmetry is spontaneously broken. In general it does not say anything about the precise form of the dispersion relation nor does it imply that there is one massless mode for each broken symmetry generator. It is a well-established fact that even for relativistic field theories in the presence of a chemical potential Goldstone modes with quadratic dispersion relation, the type II Goldstone bosons, appear in the spectrum. We develop two holographic models that feature type II Goldstone modes as part of the quasinormal mode spectrum. The models are based on simple generalizations with U(2) symmetry of the well-studied holographic s-wave superfluid. Our results include Goldstone modes without broken generators but with unusual realization of symmetries and a frequency dependent conductivity of striking resemblance to the one of Graphene.Comment: 47 pages, 21 figures; v2: references and clarifications added, typos correcte